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sdk-manual: Updates to the "Makefile-Based Projects" section.
I wrote the section to include a flow diagram using "make" and provided a working example highlighting how to override environment variables. (From yocto-docs rev: 00e8e09a51a1f0305317f38975a9d7695c92bdb5) Signed-off-by: Scott Rifenbark <srifenbark@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
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Scott Rifenbark
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Richard Purdie
Richard Purdie
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@@ -233,56 +233,118 @@
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<title>Makefile-Based Projects</title>
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<para>
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For Makefile-based projects, the cross-toolchain environment
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variables established by running the cross-toolchain environment
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setup script are subject to general <filename>make</filename>
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rules.
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Simple Makefile-based projects use and interact with the
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cross-toolchain environment variables established when you run
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the cross-toolchain environment setup script.
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The environment variables are subject to general
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<filename>make</filename> rules.
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</para>
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<para>
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To illustrate this, consider the following four cross-toolchain
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This section presents a simple Makefile development flow and
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provides an example that lets you see how you can use
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cross-toolchain environment variables to replace or override
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variables used in your Makefile.
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<imagedata fileref="figures/sdk-makefile-flow.png" width="6in" height="7in" align="center" />
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</para>
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<para>
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The main point of this section is to explain the following three
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cases regarding variable behavior:
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<itemizedlist>
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<listitem><para>
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<emphasis>Case 1 - No Variables Set in the
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<filename>Makefile</filename> that Map to Equivalent
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Environment Variables Set in the SDK Setup Script:</emphasis>
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Because matching variables are not specifically set in the
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<filename>Makefile</filename>, the variables retain their
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values based on the environment setup script.
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</para></listitem>
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<listitem><para>
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<emphasis>Case 2 - Variables Are Set in the Makefile that
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Map to Equivalent Environment Variables from the SDK
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Setup Script:</emphasis>
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Specifically setting matching variables in the
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<filename>Makefile</filename> during the build results in
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the environment settings of the variables being
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overwritten.
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In this case, the variables you set in the
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<filename>Makefile</filename> are used.
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</para></listitem>
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<listitem><para>
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<emphasis>Case 3 - Variables Are Set Using the Command Line
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that Map to Equivalent Environment Variables from the
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SDK Setup Script:</emphasis>
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Executing the <filename>Makefile</filename> from the
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command line results in the environment settings of the
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variables being overwritten.
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In this case, the command-line content is used.
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<note>
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The one exception to this is if you use the following
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command-line option:
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<literallayout class='monospaced'>
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$ make -e <replaceable>target</replaceable>
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</literallayout>
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Using the "-e" option with <filename>make</filename>
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causes the environment variables to be used during
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the build.
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</note>
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</para></listitem>
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</itemizedlist>
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</para>
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<para>
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The remainder of this section presents a simple Makefile example
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that demonstrates these variable behaviors.
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</para>
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<para>
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In a new shell environment variables are not established for the
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SDK until you run the setup script.
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For example, the following commands show null values for four
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variables that are set when you run the SDK environment setup
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script for a 64-bit build host and an i586-tuned target
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architecture for a <filename>core-image-sato</filename> image
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using the current &DISTRO; Yocto Project release:
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<literallayout class='monospaced'>
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$ echo ${CC}
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$ echo ${LD}
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$ echo ${CFLAGS}
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$ echo ${CXXFLAGS}
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</literallayout>
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Running the setup script and then echoing the variables shows the
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values established for the SDK:
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<literallayout class='monospaced'>
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$ source /opt/poky/2.5/environment-setup-i586-poky-linux
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$ echo ${CC}
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i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux
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$ echo ${LD}
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i586-poky-linux-ld --sysroot=/opt/poky/2.5/sysroots/i586-poky-linux
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$ echo ${CFLAGS}
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-O2 -pipe -g -feliminate-unused-debug-types
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$ echo ${CXXFLAGS}
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-O2 -pipe -g -feliminate-unused-debug-types
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</literallayout>
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</para>
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<para role='writernotes'>
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NEED REST OF THE EXAMPLE.
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WORKING ON GETTING IT TO WORK PROPERLY.
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</para>
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<!--
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To illustrate this, consider the following four cross-toolchain
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environment variables:
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<literallayout class='monospaced'>
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<ulink url='&YOCTO_DOCS_REF_URL;#var-CC'>CC</ulink>="i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/&DISTRO;/sysroots/i586-poky-linux"
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<ulink url='&YOCTO_DOCS_REF_URL;#var-LD'>LD</ulink>="i586-poky-linux-ld --sysroot=/opt/poky/&DISTRO;/sysroots/i586-poky-linux"
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<ulink url='&YOCTO_DOCS_REF_URL;#var-CC'>CC</ulink>="i586-poky-linux-gcc -m32 -march=i586 &DASH;&DASH;sysroot=/opt/poky/&DISTRO;/sysroots/i586-poky-linux"
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<ulink url='&YOCTO_DOCS_REF_URL;#var-LD'>LD</ulink>="i586-poky-linux-ld &DASH;&DASH;sysroot=/opt/poky/&DISTRO;/sysroots/i586-poky-linux"
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<ulink url='&YOCTO_DOCS_REF_URL;#var-CFLAGS'>CFLAGS</ulink>="-O2 -pipe -g -feliminate-unused-debug-types"
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<ulink url='&YOCTO_DOCS_REF_URL;#var-CXXFLAGS'>CXXFLAGS</ulink>="-O2 -pipe -g -feliminate-unused-debug-types"
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</literallayout>
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Now, consider the following three cases:
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<itemizedlist>
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<listitem><para>
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<emphasis>Case 1 - No Variables Set in the
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<filename>Makefile</filename>:</emphasis>
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Because these variables are not specifically set in the
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<filename>Makefile</filename>, the variables retain their
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values based on the environment.
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</para></listitem>
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<listitem><para>
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<emphasis>Case 2 - Variables Set in the
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<filename>Makefile</filename>:</emphasis>
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Specifically setting variables in the
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<filename>Makefile</filename> during the build results in
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the environment settings of the variables being
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overwritten.
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</para></listitem>
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<listitem><para>
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<emphasis>Case 3 - Variables Set when the
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<filename>Makefile</filename> is Executed from the
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Command Line:</emphasis>
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Executing the <filename>Makefile</filename> from the
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command-line results in the variables being overwritten
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with command-line content regardless of what is being set
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in the <filename>Makefile</filename>.
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In this case, environment variables are not considered
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unless you use the "-e" flag during the build:
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<literallayout class='monospaced'>
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$ make -e <replaceable>file</replaceable>
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</literallayout>
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If you use this flag, then the environment values of the
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variables override any variables specifically set in the
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<filename>Makefile</filename>.
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</para></listitem>
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</itemizedlist>
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<note>
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For information on the variables set up by the cross-toolchain
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environment setup script, see the
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@@ -290,6 +352,7 @@
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section.
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</note>
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</para>
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-->
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</section>
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</chapter>
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<!--
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